1. Field of the Invention
Embodiments of the present invention generally relate to electrochemical plating systems, and more particularly, to analyzing plating solution used in electrochemical plating systems.
2. Description of the Related Art
Metallization of sub-quarter micron sized features is a foundational technology for present and future generations of integrated circuit manufacturing processes. More particularly, in devices such as ultra large scale integration-type devices, i.e., devices having integrated circuits with more than a million logic gates, the multilevel interconnects that lie at the heart of these devices are generally formed by filling high aspect ratio interconnect features with a conductive material, such as copper or aluminum, for example. Conventionally, deposition techniques such as chemical vapor deposition (CVD) and physical vapor deposition (PVD) have been used to fill interconnect features. However, as interconnect sizes decrease and aspect ratios increase, efficient void-free interconnect feature fill via conventional deposition techniques becomes increasingly difficult. As a result thereof, plating techniques, such as electrochemical plating (ECP) and electroless plating, for example, have emerged as viable processes for filling sub-quarter micron sized high aspect ratio interconnect features in integrated circuit manufacturing processes.
In an ECP process, for example, sub-quarter micron sized high aspect ratio features formed into the surface of a substrate may be efficiently filled with a conductive material, such as copper, for example. ECP plating processes are generally two stage processes, wherein a seed layer is first formed over the surface and features of the substrate, and then the surface and features of the substrate are exposed to a plating solution, while an electrical bias is simultaneously applied between the substrate and an anode positioned within the plating solution. The plating solution is generally rich in ions to be plated onto the surface of the substrate, and therefore, the application of the electrical bias causes these ions to be urged out of the plating solution and to be plated onto the seed layer.
One particular plating parameter of interest is the chemical composition of the plating solution used in plating the substrate. A typical plating solution includes a mixture of different chemical solutions including de-ionized (DI) water. In order to obtain a desired plating characteristic across the surface of a substrate, the plating solution should include the proper concentrations of these chemical solutions. If the proper concentrations of these chemical solutions are not present in the plating fluid, the desired plating characteristic across the surface of the substrate may not be achieved. Therefore, it is desired to properly set and maintain the desired concentrations of the chemical solutions in the plating solution prior to and during the plating of the substrate.
One impediment to maintaining the desired concentrations of the chemical solutions in a plating solution during the plating cycle is that these concentrations are continuously changing. One reason for this is that the chemical solutions continuously dissipate, decompose, and/or combine with other chemicals during the plating cycle. Thus, the concentrations of the various chemicals in a plating solution will change with time if the plating solution is left alone. Accordingly, a typical ECP plating cell includes specialized devices to control the concentrations of the chemicals in the plating fluid during the plating cycle.
One such specialized device is a chemical analyzer, which is a device that probes the plating solution and periodically determines the concentrations of the chemicals in the plating solution. Using the information of the current concentrations of the chemicals in the plating solution, the chemical analyzer then determines the amount of chemicals that need to be added to the plating solution. The chemical analyzer may also determine the amount of plating solution that needs to be drained prior to adding the chemicals in order to achieve the desired concentrations for the chemicals in the plating solution.
A plating system that includes multiple plating cells may include multiple chemical analyzers, i.e., one for each plating cell. Each chemical analyzer for a given plating system may need to be calibrated together. Due the variability of each chemical analyzer and the temperature surrounding the chemical analyzer, it may be difficult to calibrate all of them to be the same. In addition, using one chemical analyzer for each plating cell within a plating system may be cost prohibitive.
Therefore, a need exists in the art for an improved system and methods for measuring chemical concentrations of a plating solution.